Researchers in the group of chemistry professor Jeff Long have developed a metal-organic-framework (MOF) material that can efficiently sort the components of gasoline. The result, a cleaner-burning mix of hydrocarbon isomers, will achieve higher octane ratings without the addition of toxic additives.
Gasoline's octane rating compares a particular blend to a standard mixture of n-heptane, a straight chain of seven carbons, and iso-octane, a highly branched molecule with eight carbons. N-heptane has an octane rating of zero, while iso-octane has a rating of 100.
In petroleum refineries, hydrocarbons with five to seven carbons are generated as a mixture of their isomers. The straight-chain, linear isomers can be removed by sieving. But low-octane monobranched isomers are difficult to sort from higher-octane dibranched isomers.
The Long group has developed a solid iron-based MOF adsorbent featuring triangular channels that can separate the desirable dibranched isomers from the less-desired monobranched and linear isomers. This MOF performs at relatively low temperatures and pressures, reducing the amount of energy required for its use, and making it more practical in refinery operations.
In the new MOF, low-octane isomers are trapped in the walls of its microscopic triangular channels, while higher octane isomers pass through. The low-octane isomers are more linear and can nestle closer to the MOF walls, making them more apt to stick to surfaces inside the MOF.
An article about the breakthrough, “Separation of hexane isomers in a metal-organic framework with triangular channels,” appears in the May 24 issue of Science magazine. The Long group and UC Berkeley have applied for a patent on the MOF, which is known by its chemical formula, Fe2(bdp)3.